Process streams in refineries are often contaminated with components that are detrimental to down-stream process units and/or are corrosive to the process equipment, or they are contaminated with solid matter, such as iron rust, which tends to interfere with process lines, valves, and pumps. The contaminants must be removed before the streams enter certain parts of the process or process units in order to maintain the process or unit performance. A filtration screen, filter housing or cartridge containing adsorbents or filtration media is usually placed in front of the process unit to remove the bulk of the undesirable matters. For example, a RONNING-PETTER multiplex filter is used to remove solid matters from atmospheric distillation residual oil before it is fed to a hydrotreater at temperatures around 200° C. Tri-cluster elements are installed in the filter to increase the filtration area. A drawback of these filtration devices is that they can be overwhelmed by large quantities of solid matters and iron rust from corrosion in a short time. As a result, processes streams frequently bypass such filtration devices as contaminant build-up cause operational problems, such as increased pressures and/or reduced flow rates. In addition, rejuvenation of conventional filtration devices requires their disassembly replacement of the filter element, which is a costly, time-consuming, and environmentally hazardous task.
Process streams in chemical plants are generally cleaner than those of refineries in terms of solid matters, but chemical streams usually contain polar components that polymerize to form solid sludge, or decompose to form more active species that cause corrosion or related problems. Activated carbon is frequently used as the adsorbent to remove the active species from the process stream. U.S. Pat. No. 4,861,900 to Johnson describes the use of activated carbon to remove small amounts of compounds that are catalyst poisons in the catalytic hydrogenation of sulfolenes to sulfolanes.
Similarly, U.S. Pat. No. 3,470,087 to Broughton describes a technique for removing polar solvent from a hydrocarbon product stream through an adsorption cycle with activated carbon and thereafter, recovering the adsorbed solvent through a desorption cycle. It has been demonstrated that adsorption-desorption arrangements with activated carbon is impractical because these units become quickly saturated with solid sludge or fine rust particles that strongly adheres to adsorbent thereby making the units difficult to clean. Other adsorbents, such alumina, silica gel and zeolitic materials have also been employed to remove polar matters from process streams. For example, U.S. Pat. No. 3,953,324 to Deal describes a method of adsorbing polar solvent with silica gel from a product stream at low temperatures and then flashing a feed mixture at higher temperatures in order to recover the adsorbed solvent from silica gel. This method encounters that same problems attendant with adsorption-desorption methods using activated carbon.
A method for removing both suspended particulate matter, such as iron rust, as well as dissolved ionic and polar impurities from a process stream is described in U.S. Pat. No. 5,053,137 to Lal. The technique entails passing a contaminated solvent, sulfolane, through a pair of columns that are arranged in series, with the first column containing cation exchanger resin and the second containing anion exchanger resin. Although this method is effective, it is not commercially feasible because only small amounts of solvent can be cleaned due to limited capacity of the ion-exchanger resins. Moreover, the procedure produces a large quantity of hazardous waste. Finally, a method that combines filtration, adsorption, and ion exchange for removing the contaminants from a liquid stream is disclosed U.S. Pat. No. 3,985,648 to Casolo. Unfortunately, the system is complex in both process design and implementation because process requires multiple ion-exchange columns, including both cation and anion exchangers, and adsorption columns.
Therefore, there is a need in the refining and chemical industries for efficient, safe, and easily regenerable filters that are particularly suited for removing contaminants that include (i) solid materials, (ii) polymerized sludge that is generated by actives in the process streams, and/or (iii) iron rust that is generated by corrosive species that attack various materials used in refining and chemical process equipment.